In the broader sense the present invention is directed to apparatus for reducing or comminuting wooden and other material into smaller sized pieces. Typically the raw feed material is waste pieces of logs, timber, or other wood based material which can then be converted into a combustible fuel source suitable for use in boilers, and the like. This is commonly known as hog fuel.
The inventor has previously described reducing apparatus in an earlier application NZ 532002 (WO2005/092509). This describes a rotatable inclined drum with an inclined reducing disc within, and seeks to provide higher quality hog fuels. However, during trials and experimentation with different materials, it was found that certain problems could sometimes arise when extending the limits of the apparatus.
These problems primarily arose when fibrous materials were present, such as certain types of vegetation, and recycled materials such as steel-belted tyres, etc. While the reducing means rapidly broke down these materials, the fibrous elements tended to accumulate within the drum rather than passing through the screening apertures. As a consequence this material would start to fill the drum, preventing new raw material from reaching the reducing means, and thus reducing the overall efficiency and throughput of the process.
In order to address these problems, and to improve the utility of the apparatus, modifications have been proposed herein. These modifications need not be restricted, however, to the apparatus of the applicant's earlier application NZ 532002. For instance it is known that the same types of problems (with fibrous and certain types of material) also affect other types of hogging apparatus. This includes tub type apparatus, where the tub is oriented substantially vertically and with the screening portions at or near the base. The applicant has proposed the use of agitators to improve screening efficiencies in these types of apparatus, in NZ patent application No. NZ532005 (published specification AU2005201329). This solution provided for agitators positioned over parts of the screen, to increase agitation and screening efficiency in these regions. However, these have limited effectiveness with fibrous materials, and their efficiencies are limited to the screen in the vicinity of the agitator.
Accordingly, it would be useful to provide an alternative solution which improves the ability of a variety of drum and tub like hoggers to deal with problematic materials, and/or improve screening efficiencies. The present invention looks at these issues.
It is therefore one object of the present invention to address at least some of the foregoing problems.
Alternatively, it is one object of the present invention to provide a drum arrangement able to more effectively deal with fibrous or lengthy type materials.
At the very least, it is an object of the present invention to provide the public with a useful alternative choice.
Aspects of the present invention will be described by way of example only and with reference to the ensuing description.